UK light-heavyweight Buatsi made a winning yet underwhelming beginning to his career under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a split decision in a close 10-round contest at the Co-op Live Arena.
But Parker found success, delivering effective individual punches in a contest where the styles failed to mesh, with constant grabbing disrupting the action.
Two judges had it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my greatest performance but how do champions respond? They succeed," the victor commented in the ring as he was met by disapproval from the crowd.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with his previous opponent in last winter - to secure a 20th pro success.
Some ringside observers thought Parker, thirty-one, should have been awarded the victory but the Derbyshire fighter endured the second setback of his 28-bout career.
Buatsi Secures Victory in Dull Match
His career development has plateaued in the past few years through promotional disputes and long spells of inactivity.
Once tipped as the future of British boxing, he now stands trying to achieve expectations - perhaps in what feels like a last chance - under new promotional backing.
He started carefully, with both competitors willing to take risks in a calculated initial rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in two years ago after suffering a hand injury in the contest, was competing in only his second bout at light-heavyweight.
By the halfway stage, the underdog had stayed in contention, creating difficulties for the favorite, who utilized a tight guard to barely take the cleaner stanzas.
The audience's tolerance diminished because of regular grabbing, with the challenger falling to the floor several times during close exchanges.
Parker ended stronger, but many rounds were difficult to score. Nevertheless, previous titleholder Carl Frampton - providing analysis for Dazn - had it strongly leaning for Parker, scoring for Buatsi just a single round.
The victor progresses, but with the presence of power puncher David Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Hatton Memorial Motivates Manchester Derby Contest
In the secondary fight, Arthur beat Rea by divided decision in a terrific local rivalry contest to capture the continental belt.
The venue grew hushed for a extremely emotional memorial ahead of the contest as 10 bells sounded in remembrance of Manchester's own Hatton, who passed away at age 46 in last month.
It was the first major televised fight night in the city since the passing of Hatton. As the final chime faded, the stillness gave way to a roar of "only one Ricky Hatton".
The competition during the bout reflected the emotion. Arthur was floored by a powerful punch squarely on the jaw in the early round, getting up unsteadily to his footing on the referee's count.
But the Manchester United-red equipment of Arthur soon came forward again. Across the ring, the opponent - in competitive blue - was damaged soon, significant bruising forming under his face as the pair traded powerful shots.
Rea, twenty-seven, landed power punches but the champion, 34, matched the intensity with powerful upward punches as the action rarely dropped over twelve rounds.
The victor barely secured the verdict with official scores of draw, close margin and wider gap, but the two athletes were determined and brave, all the qualities their hero the legend embodied.
